Scraped surface heat exchanger for continuous heating or cooling of viscous masses

ABSTRACT

A heat exchanger, preferably a scraped surface heat exchanger, is designed to heat or cool viscous or highly viscous material. The heat exchanger is equipped with a product cylinder ( 3 ) surrounded by a heat transfer medium and containing a rotationally driven shaft ( 2 ). The shaft and the product cylinder form a gap ( 10 ) with an annular cross-section for receiving the material to be treated. To avoid the use of coolant substances that are harmful to the environment or the operator, Peltier elements ( 5 ) are arranged between the heat transfer medium and the product cylinder ( 3 ) on the side of the cylinder facing away from the annular gap ( 10 ). The Peltier elements cool the material to be treated on the secondary side, enabling water to be used as the coolant, the water posing no threat to the environment and being re-cooled without difficulty in water towers. The cooling process takes advantage of the effect of the thermal pump of the Peltier element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/DE2003/003910, filed Nov. 25, 2005, which was published in the German language on Jun. 17, 2004, under International Publication No. WO 2004/051159 A1 and the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a scraped surface heat exchanger for continuous heating or cooling of viscous masses, the heat exchanger having a product cylinder surrounded by a heat transfer medium and a rotationally driven shaft arranged in the product cylinder with a gap space of annular cross section between the shaft and the product cylinder for receiving a mass to be treated.

Such a heat exchanger, particularly a scraped surface heat exchanger, is known from European Patent EP 0 727 634 B1. With this known heat exchanger the product to be treated and temperature-controlled is pumped through a product cylinder. If the heat exchanger is applied for cooling, then as a heat transfer medium for the quantity of heat to be led away, one applies chilled water, glycol or sols on the secondary side, or a directly evaporating, liquid Freon or ammonia is used. The media Freon and ammonia are not only a danger to the environment, but also to persons who operate devices with such heat exchangers.

BRIEF SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide a heat exchanger of the type mentioned above, which avoids the application of substances that endanger the environment or are a danger to the user.

This object is achieved by arranging Peltier elements between the heat transfer medium and the product cylinder on a side of the product cylinder facing away from the annular gap space. Advantageous embodiments of the invention are described in the following description.

According to the invention, the technology of the Peltier element which is known per se is applied, wherein with a corresponding technical application one may use several Peltier elements. With the heat exchanger according to the invention, the discharge of the heat quantity, which is to be led away, is effected almost exclusively by way of the Peltier element. It is thereby possible to use common cooling water, whose exit temperature lies above the temperature of the surroundings. This cooling water is simple to prepare in conventional cooling towers.

The heat exchanger according to the invention is envisaged for continuous heating or cooling of viscous or highly viscous masses. It comprises a product cylinder which is surrounded by a heat transfer medium and in which a rotationally driven shaft is arranged, with which the product cylinder forms a gap space of annular cross section for receiving the mass to be treated. The basic concept of the present invention is to arrange Peltier elements between the heat-transfer medium and the product cylinder on a side away from the annular gap space. The Peltier elements may be attached to the product cylinder in a practically complete-surfaced manner, so that a good heat transfer is ensured.

Preferably the Peltier elements form a heat pump if the heat exchanger is used for cooling. However, they may also be applied, where appropriate, for heating by changing the polarity of the voltage supply.

It is particularly beneficial if the Peltier elements are arranged in an annular gap through which the heat transfer medium flows, the gap being formed on the one hand by the product cylinder and on the other hand by an outer cylinder surrounding the gap. Here, the Peltier elements may be advantageously covered by a casing of heat-conductive material, preferably copper. In this manner, the Peltier elements are protected with respect to the heat transfer medium and on the other hand are connected to the medium in a good heat-conducting manner. One may omit a heat-conductive, protective casing if the Peltier elements are designed to be suitably corrosion-resistant.

It is advantageous if the product cylinder over its whole periphery is formed as a Peltier element, since then a very uniform and at the same time intensive cooling effect or heating effect may be achieved.

According to a further embodiment of the invention, the complete product cylinder or parts thereof on the side facing the Peltier elements may comprise one or more plane surfaces which are designed for receiving Peltier elements which are designed with a plane surface. Such a design is favorable if planar Peltier elements are much more economically available than those envisaged for attachment onto a cylinder surface. Alternatively, one may also here provide suitably good heat-conducting adapter pieces, which have a cylindrical curvature on one side a planar surface on the other side.

The annular gap space of a scraped surface heat exchanger in which the masses to be treated are accommodated is advantageously provided with scraper knives, which are fastened on the rotationally driven shaft and contact the surface of the cylinder at its inner side. On rotation of the shaft the scraper knives continuously scrape away the viscous mass, in order to allow thereby a good heat transfer between the cylinder wall and the mass to be treated in the gap space. This is useful, in particular, if substances are to be processed which form an insulating layer on the surface which faces the medium, on account of their crystallizing or highly viscous properties. In an advantageous manner the invention may thus be applied with so-called scraped surface heat exchangers which are equipped with scraper knives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

FIG. 1 is a perspective view of a scraped surface heat exchanger according to one embodiment of the invention; and

FIG. 2 is a longitudinal section through an embodiment according to the invention, but without showing a rotationally driven shaft or scraper knives.

DETAILED DESCRIPTION OF THE INVENTION

The heat exchangers serve for heating or cooling various substances, preferably however foodstuffs, for example margarine, mayonnaise and starches. Creams and ointments may also be treated.

With the represented embodiment, so-called Peltier elements 5 are applied, in particular for thermoelectric cooling. The Peltier effect is based on the fact that with a two-conductor circuit of a thermoelement, through which current flows, one thermojunction is cooled and the other is heated. The electrical current, with an initially uniform temperature of the conductor circuit, thus produces a temperature drop between the thermojunctions. The invention exploits this effect in order to lead away heat at the secondary side of the product cylinder 3, that is, on the side that faces away or is remote from the annular gap space 10.

The invention in principle may be used for cooling or for heating. In the following a scraped surface heat exchanger for cooling a mass to be treated is described as an example which is represented in the drawings.

The mass to be treated is pumped through an annular gap space 10 between a rotationally driven shaft 2 and a product cylinder 3. Scraper knives 1 which are fastened on the shaft 2 scrape the product to be treated from the inner wall of the product cylinder 3 and thus ensure a circulation and a correspondingly improved heat transfer.

A number of Peltier elements 5, which basically may be connected in series or in parallel, are arranged on the outer side of the product cylinder 3. The electrical supply leads run through the gap 4 and to the outside at 12 in FIG. 2. The Peltier elements 5 are covered and protected by an outer casing 6 of heat-conductive material, for example copper sheet. This unit of the Peltier elements 5 and the outer casing 6 lies within an external cylinder 8, which is rinsed-through by the heat transfer medium. This heat transfer medium enters at 14 and exits at 15. The annular gap in which the unit of Peltier elements 5 and heat-conductive casing 6 lies is indicated at 7. Seals 9 seal the end-faces of this space in which the Peltier elements 5 lie. A seal 16 seals the annular gap 7 with respect to the product cylinder 3. A flange 13 is located on the other side, and this flange with a seal 11 ensures a sealing with respect to a corresponding flange of the outer cylinder 8.

In operation, the mass to be treated is pumped through the annular gap space 10 between the product cylinder 3 and the shaft 2. Electrical current flows through the Peltier elements 5 in a manner such that the known cooling effect occurs. The heat which arises at the same time on the surface of the Peltier elements 5 lying opposite to and remote from the gap space 10 is led away by the heat transfer medium in the annular gap 7. A fine adjustment is possible by way of the application of Peltier elements 5 which may be controlled by the control of the electrical current.

The Peltier elements 5 may also be applied as a full-surfaced coating instead of as individual elements. An even more uniform and gapless management of the temperature level is thereby achieved.

The Peltier elements 5 may also be applied without heat-conductive copper protection casing 6, insofar as the elements are manufactured of corrosion-resistant materials or are provided with such.

The cylinder 3 on the side facing the Peltier elements may also have axially running planar surfaces instead of a cylindrical shape. This feature provides the advantage that planar Peltier elements may be deposited.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims. 

1. A scraped surface heat exchanger for continuous heating or cooling of viscous masses, the heat exchanger comprising a product cylinder (3) surrounded by a heat transfer medium and a rotationally driven shaft (2) arranged in the product cylinder (3) with a gap space (10) of annular cross section between the shaft (2) and the product cylinder (3) for receiving a mass to be treated, wherein Peltier elements (5) are arranged between the heat transfer medium and the product cylinder (3) on a side of the product cylinder facing away from the annular gap space (10).
 2. The heat exchanger according to claim 1, wherein the Peltier elements (5) are applied as heat pumps for cooling or, by reversal of a voltage supply to the Peltier elements, for heating the mass to be treated.
 3. The heat exchanger according to claim 1, wherein the Peltier elements (5) are arranged in an annular gap (7) through which the heat transfer medium flows and which is formed by the product cylinder (3) and an outer cylinder (8) surrounding the product cylinder.
 4. The heat exchanger according to claim 1, wherein the Peltier elements (5) are covered by a casing (6) of heat-conductive material.
 5. The heat exchanger according to claim 1, wherein the entire product cylinder (3) is designed as a Peltier element.
 6. The heat exchanger according to claim 1, wherein the entire product cylinder (3) on a side facing the Peltier elements (5) is designed with a plurality of axial, planar surfaces for accommodating planar Peltier elements.
 7. The heat exchanger according to claim 1, comprising a scraped surface heat exchanger.
 8. The heat exchanger according to claim 7, wherein scraper knives (1) are fastened on the rotationally driven shaft (2) in the annular gap space (10) for receiving the mass to be treated, and wherein the scraper knives (1) contact and scrape the surface of the cylinder (3). 